Now my FIL only eats sweet food. He refused to take on regular food. But if the caregiver feeds him by spoon (all pureed) he would eat it nicely.

Is this a form of refusing food by not taking it? It is still OK that he can be fed. Is it because he does not think regular food is food and is not tasty?
There is a scientific article that indicates AD patient in the end likes sweets more than salt because of the way the brain works.

He is not taking Ensure yet because the NH believes in pureed food first. But now it takes longer to feed him.
Sometimes they may feed him later after everyone is served. Or they wait to see if he can do it himself. But he has not done so since April.